In linear multicapillary array-based DNA sequencing machines, a laser beam irradiates individual capillaries of the array, and a multipixel photodetector collects the resulting fluorescence of fluorophore-labeled DNA fragments in the capillaries. Increasing the number of simultaneously operated capillary lanes can significantly increase the throughput of DNA sequencing machines. Side-irradiation or -illumination of linearly arrayed capillaries is convenient and is thus widely used in the design of modern sequencers. However, reflection and refraction of the laser beam at the walls of individual capillaries causes nonuniform illumination of the capillary channels. Thus, there is a need for devices and methods that maximize illumination but minimize reflection and refraction of the laser beam to maximize the number of capillaries that can be utilized.